Electric water heaters have been able for many years and generally comprise a tank containing a body of water, an electric heating element disposed within the tank to heat the water, a water inlet, a water outlet and a thermostat to control the application of electrical current to the heating element. Generally, the tank has been metallic and the thermostat has been held against this tank by means of a mounting bracket. One such arrangement is described in U.S. Pat. No. 4,657,215 to Murphy. Murphy describes a bracket which mounts upon a fitting welded to the water containing tank and urges the thermostat into intimate contact with the water containing tank. In this way, the thermostat senses the temperature of the water through the tank wall. Because the tank wall is metallic, it is a good conductor of heat. The tank wall is also generally thin so the sensor adequately monitors the water temperature.
Attempts have been made to manufacture electric water heaters using plastic tanks. Problems have been encountered. One problem is sensing of water temperature by a thermostat. One can put a fitting in the side of a plastic tank in a manner similar to a metal tank and apply a surface thermostat to the plastic tank as illustrated in Murphy U.S. Pat. No. 4,657,215. However, temperature sensing is not adequate. Moreover, such an approach requires a breach in the integrity of the side wall of the plastic tank which compromises its strength.
The present invention contemplates a new and improved water heater structure using a plastic tank which overcomes the above-referred to problems and others, and provides a water heater in which a thermostat reliably and accurately senses water temperature while maintaining tank integrity.